Electronic structure and hybridization of CaS by means of X-ray absorption spectroscopy at Ca and S K-edges

Abstract

The cubic calcium sulfide (CaS) is a well known system and an attractive building block material for many luminescence technological applications. However, it is essential to achieve an accurate understanding of its electronic structure in order to engineer its band structure for optimized applications. Here a study of the electronic structure of CaS by means of X-ray absorption spectroscopy performed at both Ca and SK-edges, and calculations performed in the framework of the multiple-scattering theory and of the finite difference method are presented. At the CaK-edge the presence of an anomalousdstates feature is discussed while in the SK-edge spectrum the presence of a pre-edge shoulder owing to the hybridization among Cadstates and Spstates is pointed out. Although thel-projected density of states of CaS is in good agreement with previous first-principles calculations, the standard muffin-tin potential is inadequate to reproduce near-edge structures at both Ca and SK-edges in this system. Indeed, with its highly symmetric and less compact structure, CaS is characterized by a large set of collinear atomic configurations that pose severe constraints on the construction of the atomic potential. On the contrary, the finite-difference method with no muffin-tin approximation is more suitable for X-ray absorption calculations in this system.